Concentrator systems are emerging as a low-cost, high-volume option for solar-generated electricity due to the very high utilization of the solar cell, leading to a much lower $/Watt cost of a photovoltaic system. Parallel to this is the onset of alternative solar cell technologies, such as the very high efficiency multi-junction solar cells developed at NREL and Spectrolab over the last two decades. The relatively high cost of these types of solar cells has relegated their use to non-terrestrial applications. However, recent advancements in both multi-junction concentrator cell efficiency and their stability under high flux densities has made their large-scale terrestrial deployment significantly more viable. Amonix has designed, developed and fabricated modules using the high efficiency multi-junction cells from Spectrolab. One of these modules has been deployed at the University of Nevada, Las Vegas. The module has been in continuous operation beginning May 2006. The efficiency has been measured periodically and has shown a range from 26.1% to 28.5%. The latest measurement, made on February 20th showed an efficiency of 28.0 % at 956 DNI and an ambient temperature of 13 °C. This excellent stability of the multi-junction module's performance promises to pave the way for future installations of this advanced technology. One short-term example of this is a new Amonix-designed module capable of 30% efficiency and 300 Watts per module. This module's performance, along with more testing of the long-term performance of the initial design will be presented at the time of the conference.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.